Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$201.61	6.425%	$214.5634	$214.56	$214.55	$214.60
Purchase #2	$79.84	12.133%	$89.527	$89.53	$89.55	$89.50
Purchase #3	$82.67	8.780%	$89.9284	$89.93	$89.95	$89.90
Purchase #4	$39.97	12.754%	$45.0678	$45.07	$45.05	$45.10
Purchase #5	$41.51	5.465%	$43.7785	$43.78	$43.80	$43.80
Purchase #6	$149.58	7.606%	$160.9571	$160.96	$160.95	$161.00
Purchase #7	$23.98	8.387%	$25.9912	$25.99	$26.00	$26.00
7 purchase totals =	$619.16		$669.8134	$669.82	$669.85	$669.90